<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>盒子模型</title>
    <style>
        .fa{
            width: 500px;
            height: 300px;
            background: pink;
            padding: 10px;
            margin: 20px;
            border: 5px dashed red;
        }
    </style>
</head>
<body>
    <div class="fa"></div>
</body>
</html>